Regenerable biocide delivery unit

ABSTRACT

A method and apparatus are disclosed for maintaining continuous, long-term microbial control in the water supply for potable, hygiene, and experimental water for space activities, i.e., space shuttle, orbiter lab, Lunar base, Mars base, deep space missions, etc., as well as treatment of water supplies on earth. The water purification is accomplished by introduction of molecular iodine into the water supply to impart a desired iodine residual. The water is passed through an iodinated anion exchange resin bed. The iodine is bound as I -   n  at the anion exchange sites and releases I 2  into the water stream flowing through the bed. Suitable anion exchange resins are Amberlite IRA 401S (Rohm &amp; Haas); Dowex SBR (Dow Chemical); and Ionac ASB-1P (Sybron Corp.). The concentration of I 2  in the flowing water gradually decreases and the ion-exchange bed has had to be replaced. In a preferred embodiment, a bed of iodine crystals is provided with connections for flowing water therethrough to produce a concentrated (substantially saturated) aqueous iodine solution which is passed through the iodinated resin bed to recharge the bed with bound iodine. The iodinated resin bed has been recharged up to eight times during continuous use to permit an extended life to the system. The bed of iodine crystals is connected in parallel with the iodinated resin bed and is activated periodically, e.g., by timer, by measured flow of water, or by iodine residual level, to recharge the bed.

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract, and is subject to the provisions of Public Law 96-517(35 USC §202 et seq.) in which the Contractor has elected not to retaintitle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to water purification systems and moreparticularly to a water purification accomplished by introduction ofmolecular iodine into the water supply to impart a desired iodineresidual by use of an iodinated exchange resin bed which is rechargedperiodically during use.

2. Brief Description of the Prior Art

The use of chlorine for water purification is well known. Iodine hasalso been used for the same purpose.

In space activities, i.e., space shuttle, orbiter lab, Lunar base, Marsbase, deep space missions, etc., continuous, long-term microbial controlin the water supply for potable, hygiene, and experimental water hasbeen accomplished by introduction of molecular iodine into the watersupply to impart a desired iodine residual. The water is passed throughan iodinated anion exchange resin bed which releases molecular iodine.

Lambert and Fina U.S. Pat. Nos. 3,817,860 and 3,923,366 disclose methodsof disinfecting water and demand bacteriacides but do not show in situregeneration.

Barnes U.S. Pat. No. 4,888,118 discloses a water purification process inwhich the water is passed through a mass of nylon 4 complexed withiodine. The treated water is subsequently passed through nylon 4 toremove iodine from the water. The nylon 4 used in both treatment zonescan be in any form, preferably a form having a high surface area, e.g.,powder, fiber, drawn or undrawn, staple fiber, knitted or non-wovenfabrics or pulp fibrils.

Keblys et al U.S. Pat. No. 4,131,645 discloses an iodine recoveryprocess by repeated cycles of passing an iodine-containing brine througha basic ion exchanger to absorb iodine and then oxidizing adsorbediodide to iodine by passing an acidified aqueous iodate solution throughthe exchange resin.

Abrams U.S. Pat. No. 4,849,111 discloses a method and apparatus forregenerating a dynamic adsorber system which removes a contaminant froma fluid. The bed is periodically cleansed by flowing a clean fluidtherethrough.

The present invention is distinguished over the prior art in general,and these patents in particular by a method and apparatus disclosed formaintaining continuous, long-term microbial control in the water supplyfor potable, hygiene, and experimental water for space activities, i.e.,space shuttle, orbiter lab, Lunar base, Mars base, deep space missions,etc., as well as various terrestrial applications. The waterpurification is accomplished by introduction of molecular iodine intothe water supply to impart a desired iodine residual. The water ispassed through an iodinated anion exchange resin bed. The iodine isbound as I_(n) ⁻, where n is an odd integer greater than three, at theanion exchange sites and releases I₂ into the water stream flowingthrough the bed. Suitable resins are strong base anion exchange resinssuch as AMBERLITE IRA 401S (Rohm & Haas); DOWEX SBR (Dow Chemical); andIONAC ASB-1P (Sybron Corp.). The concentration of I₂ in the flowingwater gradually decreases and the ion-exchange bed has had to bereplaced. In a preferred embodiment, a bed of iodine crystals isprovided with connections for flowing water therethrough to produce aconcentrated (substantially saturated) aqueous iodine solution which ispassed through the iodinated resin bed to recharge the bed with boundiodine. The iodinated resin bed has been recharged up to eight timesduring continuous use to permit an extended life to the system. The bedof iodine crystals is connected in parallel with the iodinated resin bedand is activated periodically, e.g., by timer, by measured flow ofwater, or by iodine residual level, to recharge the bed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a new andimproved method and apparatus for maintaining continuous, long-termmicrobial control in the water supply for potable, hygiene, andexperimental water for space activities, i.e., space shuttle, orbiterlab, Lunar base, Mars base, deep space missions, etc., as well asterrestrial applications.

It is another object of this invention to provide a new and improvedwater purification process or method by introduction of molecular iodineinto the water supply to impart a desired iodine residual.

Another object of this invention is to provide a new and improved waterpurification process or method by introduction of molecular iodine intothe water supply to impart a desired iodine residual wherein the wateris passed through an iodinated anion exchange resin bed.

Another object of this invention is to provide a new and improved waterpurification by introduction of molecular iodine into the water supplyto impart a desired iodine residual wherein the water is passed throughan iodinated anion exchange resin bed in which the iodine is bound asI_(n) ⁻, where n is an odd integer greater than three, at the anionexchange sites and releases I₂ into the water stream flowing through thebed.

Still another object of this invention is to provide a new and improvedwater purification by introduction of molecular iodine into the watersupply to impart a desired iodine residual wherein the water is passedthrough an iodinated anion exchange resin bed, preferably AMBERLITE IRA401S (Rohm & Haas); DOWEX SBR (Dow Chemical); and IONAC ASB-1P (SybronCorp.), in which the iodine is bound as I_(n) ⁻, where n is an oddinteger greater than three, at the anion exchange sites and releases I₂into the water stream flowing through the bed.

Still another object of this invention is to provide a new and improvedwater purification by introduction of molecular iodine into the watersupply to impart a desired iodine residual wherein the water is passedthrough an iodinated anion exchange resin bed, the concentration of I₂in the flowing water gradually decreases and the ion-exchange bed isrecharged by treatment with a strong aqueous iodine solution.

A further object of this invention is to provide an improved waterpurification by introduction of molecular iodine into the water supplyto impart a desired iodine residual wherein the water is passed throughan iodinated anion exchange resin bed, the concentration of I₂ in theflowing water gradually decreases and the ion-exchange bed is rechargedby treatment with an aqueous iodine solution produced by flowing waterthrough a bed of iodine crystals having connections in parallel with theion-exchange bed.

A further object of this invention is to provide an improved waterpurification by introduction of molecular iodine into the water supplyto impart a desired iodine residual wherein the water is passed throughan iodinated anion exchange resin bed, the concentration of I₂ in theflowing water gradually decreases and the ion-exchange bed is rechargedby treatment with an aqueous iodine solution produced by flowing waterthrough a bed of iodine crystals having connections in parallel with theion-exchange bed and activated periodically, e.g., by timer, by measuredflow of water, or by iodine residual level, to recharge the bed.

Other objects of the invention will become apparent from time to timethroughout the specification and claims as hereinafter related.

The above noted objects and other objects of the invention areaccomplished by a novel apparatus for maintaining continuous, long-termmicrobial control in the water supply for potable, hygiene, andexperimental water for space activities, i.e., space shuttle, orbiterlab, Lunar base, Mars base, deep space missions, etc., as well asvarious terrestrial applications. The water purification is accomplishedby introduction of molecular iodine into the water supply to impart adesired iodine residual. The water is passed through an iodinated anionexchange resin bed. The iodine is bound as I_(n) ⁻, where n is an oddinteger greater than three, at the anion exchange sites and releases I₂into the water stream flowing through the bed. Suitable anion exchangeresins are AMBERLITE IRA 401S (Rohm & Haas); DOWEX SBR (Dow Chemical);and IONAC ASB-1P (Sybron Corp.). The concentration of I₂ in the flowingwater gradually decreases and the ion-exchange bed has had to bereplaced. In a preferred embodiment, a bed of iodine crystals isprovided with connections for flowing water therethrough to produce aconcentrated (substantially saturated) aqueous iodine solution which ispassed through the iodinated resin bed to recharge the bed with boundiodine. The iodinated resin bed has been recharged up to eight timesduring continuous use to permit an extended life to the system. The bedof iodine crystals is connected in parallel with the iodinated resin bedand is activated periodically, e.g., by timer, by measured flow ofwater, or by iodine residual level, to recharge the bed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a water purification system wherein thewater is passed through an iodinated anion exchange resin bed.

FIG. 2 is a flow diagram of a water purification system wherein thewater is passed through an iodinated anion exchange resin bed and a bedof iodine crystals has connections for flowing water therethrough toproduce a concentrated (substantially saturated) aqueous iodine solutionwhich is passed through the iodinated resin bed to recharge the bed withbound iodine, the bed of iodine crystals being connected in parallelwith the iodinated resin bed and activated periodically, e.g., by timer,by measured flow of water, or by iodine residual level, to recharge thebed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings by numerals of reference, and moreparticularly to FIG. 1, there is shown a flow diagram of a system forpurification of water by passing water from a water recovery system 10through a bed 11 of iodinated anion exchange resin to storage and use12. The bed 11 is a container having an inlet and an outlet whichcontains the iodinated anion exchange resin.

The anion exchange resins 13 used in the exchange resin bed is a strongbase ion exchange resin. These resins have amine or quaternary aminesites on the resin backbone which is generally of the polystyrene type.The more preferred resins are the strongly basic anion exchange resinssuch as those having a quaternary ammonium site, e.g., polystyrenetrimethylammonium chloride resins. A useful resin of this type is DOWEXSBR (Dow Chemical), although other strong base anion exchange resinssuch as AMBERLITE IRA 401S (trademark of Rohm and Haas Co.); and IONACASB-1P (Sybron Corp.) could be used.

When these anion exchange resins are treated with iodine untilcompletely iodinated, iodine is bound at the basic sites in the resin inthe form of I_(n) ⁻, where n is an odd integer greater than three. Whenwater is passed through the iodinated exchange resin bed, as shown inFIG. 1, molecular iodine (I₂) is washed out of the resin slowly toproduce an effective I₂ residual in the flowing water leaving I⁻ at thebasic sites in the resin.

Over a period of time, the iodine content of the resin decreases and theI₂ residual in the effluent water drops markedly. A long term washouttest was conducted with a 3.8 cc. bed of AMBERLITE IRA 401S (trademarkof Rohm & Haas Co.) using a water flow rate of 8.5 ml./min. at 70° F.The I₂ residual in the effluent water is set forth in Table I below.

                  TABLE I                                                         ______________________________________                                        401S IODINATED RESIN WASHOUT                                                  ______________________________________                                        Throughput liters/cc.                                                                      0     10     20   30   40   50   60                              I.sub.2 resid. mg./l.                                                                      4.4   3.0    2.0  1.6  1.2  1.1  1.0                             ______________________________________                                    

Over the period of this test, the I₂ residual decreased to a point whereit was necessary to replace the resin.

In long duration programs such as Pathfinder and Space Station Freedom,it is necessary to have closed loop life support technology thatprovides long-term life support at minimum resupply costs. In the SpaceStation Freedom, 20 installations of the iodinated exchange resin bedshave been identified, each with a 90 day life. In 30 years of proposedoperation, the station would require 2,400 replacement units for waterpurification. This problem has led to the development of the system ofregeneration described below.

In preparation for testing a process for regeneration of the iodinatedexchange resin, determinations were made of iodine solubility in wateras in Table II below.

                  TABLE II                                                        ______________________________________                                        SOLUBILITY OF IODINE IN WATER                                                 Temp. °C.                                                                        I.sub.2 mg./l.                                                                             Temp. °C.                                                                        I.sub.2 mg./l.                               ______________________________________                                         0        162          60        1,060                                        20        293          70        1,510                                        25        340          80        2,170                                        30        399          90        3,120                                        40        549          100       4,480                                        50        769                                                                 ______________________________________                                    

Next, tests, were run on the dissolution of iodine in water flowingthrough a regeneration bed. The regeneration bed is a container havingan inlet and an outlet which contains the iodine crystals. Smallregeneration beds were prepared, viz., 1.7 cc., 3.3 cc. and 5.0 cc.,loaded loosely with iodine crystals, 3.8 g., 8.0 g. and 11.5 g.,respectively, and water passed therethrough at a flow rate of 8.5ml./min. The effluent I₂ concentration was measured directly at 460 nmusing a Beckman DB spectrophotometer as reported in Table III.

                  TABLE III                                                       ______________________________________                                        CRYSTALLINE IODINE BED WASHOUT                                                ______________________________________                                        5.0 cc.                                                                       Bed                                                                           Thru-  5      10     15  20   25   30   35   40   45                          put -                                                                         liters                                                                        mg.   260    270    250  240  225  200  150  120  70                          I.sub.2 /l.                                                                   3.3 cc.                                                                       Bed                                                                           Thru-  5      10     15  20   25   30   35   40   45                          put -                                                                         liters                                                                        mg.   220    250    200  175  140  80   50                                    I.sub.2 /l.                                                                   1.7 cc.                                                                       Bed                                                                           Thru-  5      10     15  20   25   30   35   40   45                          put -                                                                         liters                                                                        mg.   180    200    120  50   25                                              I.sub.2 /l.                                                                   ______________________________________                                    

Further tests relating specific conductance, pH and effluent I₂concentration showed that effluent iodine levels from the regenerationbed are insensitive to influent conductivity. A determination of theeffect of residence time of water in the regeneration bed showed aneffluent iodine concentration of 200 mg/l. at 0.2 min., 250 mg./l. at0.4 min., and 270 mg./l. at 0.6 min. residence time in bed.

In FIG. 2, there is shown a flow diagram of a system for purification ofwater by passing water from a water recovery system 14 through a bed 15of iodinated anion exchange resin 16 to storage and use 17.

As in FIG. 1, the anion exchange resins 17 used in the exchange resinbed is a strong base ion exchange resin. These resins have amine orquaternary amine sites on the resin backbone which is generally of thepolystyrene type. The more preferred resins are the strongly basic anionexchange resins such as those having a quaternary ammonium site, e.g.,polystyrene trimethylammonium chloride resins. A useful resin of thistype is AMBERLITE IRA 401S (trademark of Rohm and Haas Co.), althoughother strong base anion exchange resins such as DOWEX SBR (DowChemical); and IONAC ASB-1P (Sybron Corp.) could be used. The bed 15 isa container having an inlet and an outlet which contains the iodinatedanion exchange resin.

Regeneration of the resin bed 15 was carried out using the datadeveloped above. A regeneration bed 18 containing iodine crystals 19 (acontainer having an inlet and an outlet which contains the iodinecrystals) is connected in parallel to iodinated exchange resin bed 15 byconduits 20 and 21. An automatically operated three-way valve 22connects water supply 14 to conduit 20 leading to regeneration bed 18and to conduit 23 connecting to iodinated exchange resin bed 15. Acontroller 24 having an optional connection 25 to a sensor in storageline 17 controls valve 22. Three way valve 22 has a normal positiondirecting water flow to iodinated exchange resin bed 15 and shutting offflow to regeneration bed 18.

Controller 24 is operable periodically to turn three way valve 22 to aposition directing water flow through regeneration bed 18 and shuttingoff flow directly to iodinated exchange resin bed 15. Automaticcontroller, shown schematically at 24, may be a timer to operate valve22 at timed intervals or may be responsive to volume of water passingthrough iodinated exchange resin bed 15 or to the iodine residual in thewater flowing to storage 17 to operate valve 22 after a predeterminedvolume of water flow or a predetermined drop in I₂ residual. Theoperation of valve 22, as described, shifts the path of water flow froma direct path into iodinated exchange resin bed 15 to a path throughregeneration bed 18 and then into iodinated exchange resin bed 15, aftera predetermined time or after a predetermined flow of water throughiodinated exchange resin bed 15 or after a predetermined drop in I₂residual.

A long term test of the above equipment was carried out to test theregeneration concept. The switching of the water flow between directflow through resin bed 15 and flow through regeneration bed 18 intoresin bed 15 was performed manually based on I₂ residual data obtainedon the effluent during the test.

The system was operated 24 hours per day for 114 days. The total waterprocessed was 1,236 liters. The average effluent I₂ concentration as 2.9mg./1. The regeneration bed 18 initially contained 5.0 cc. (9.0 g.)iodine crystals. The exchange resin bed 15 contained 2.5 cc. ofiodinated AMBERLITE IRA 401S. The water flow rate was 8.5 cc./min. Thisflow rate corresponds to a contact time that is 33% less than the designvalue for use in the NASA shuttle in order to expedite the test. For theexchange resin bed 15, the effluent iodine concentration is independentof flow rate. However, a higher exchange resin bed 15 effluent isachieved using a higher flow rate during the regeneration step.

The I₂ residual in the effluent was monitored and plotted against litersof water throughput. When the residual dropped from 4.0 to about 1.0,the flow was switched through the iodine-containing regeneration bed 18and then through exchange resin bed 15 for about 0.8 min. until theresin was re-iodinated to at least the initial iodine level. After theresin bed 15 was regenerated, the water flow was switched back to directflow through bed 15 and the monitoring of iodine residual continued.

At the start of the test, the exchange resin bed 15 contained 3.8 cc.resin and the effluent iodine content was 4.0 mg./l. After a throughputof 197 liters, the resin bed volume was reduced to 2.5 cc. for theremainder of the test to increase the number of regenerations that couldbe obtained during the 32/3 months test. A total of 8 regenerations wereaccomplished, and none of the data indicated that the exchange resincould not be regenerated further. Each of the regenerations raised theiodine content of the resin bed 15 sufficiently to produce an I₂residual in the water effluent in excess of the initial values of 4.0mg./l. The first five regenerations were performed at an acceleratedflow rate and a regeneration spike was observed that reached a maximumvalue of 6-11 mg./l. residual I₂. Regenerations were done after a dropin I₂ residual to about 1.0 mg./l, at water throughputs of 200 l., 300l., 500 l., 670 l., and 800 l., respectively. For the last threeregenerations, at water throughputs of 980 l., 1080 l., and 1,200 l.,respectively, the flow rate during regeneration was reduced to 3.0ml./min., a residence time of 0.8 min. in bed 15 which eliminated thespike. The residence time of 0.8 min. has been found adequate toregenerate resin bed 15 to the initial iodine level.

This long term test has proved the feasibility of repeated regenerationof the resin bed 15. The life of the resin bed 15 was increased by afactor of eight with no decrease in performance. The life of resin bed15 was increased from 60 l. water per cc. of iodinated resin to 500 l.per cc. Eight regenerations were performed consuming 3.57 g. iodine. Itwas not possible to project the ultimate life of resin bed 15 since nophysical attrition, dysfunction or inconsistencies in performance werenoted. At the end of the 114 day test, the resin was fully charged,producing 4.0 mg./l I₂ residual. The test has demonstrated that thesystem is operative for long term water purification in closed loop lifesupport systems such as those in space shuttle, orbiter lab, Lunar base,Mars base, Pathfinder, Space Station Freedom, deep space missions, etc.

While this invention has been shown fully and completely with specialemphasis on certain preferred embodiments, it should be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described herein.

We claim:
 1. A method of treating water to produce a predetermined I₂ residual therein comprisingproviding a bed of anion exchange resin iodinated to a selected iodine content, flowing water requiring purification through said iodinated anion exchange resin to remove iodine from said resin and produce said predetermined I₂ residual therein, continuing flowing said water through said bed of anion exchange resin until the effluent iodine content is reduced to a selected lower level, preparing an aqueous solution of I₂, passing said solution through said bed to re-iodinate said resin to said selected iodine content, and flowing further amounts of water requiring purification through said iodinated anion exchange resin to remove iodine from said resin and produce said predetermined I₂ residual therein.
 2. A method according to claim 1 in whichsaid resin is iodinated to a level sufficient to produce an I₂ residual in excess of 1.0 mg./liter in water passing therethrough.
 3. A method according to claim 1 in whichsaid iodine solution contains at least 1 mg. I₂ per liter.
 4. A method according to claim 1 in whichsaid iodine solution is prepared and passed through said resin bed continuously during the regeneration step.
 5. A method according to claim 1 includingproviding a bed of iodine crystals, continuously passing water through said iodine crystals to produce said iodine solution and continuously passing said iodine solution through said resin bed during the regeneration step.
 6. A method according to claim 1 includingproviding a bed of iodine crystals, continuously passing water through said iodine crystals to produce said iodine solution containing at least 1 mg. I₂ per liter, and continuously passing said iodine solution through said resin bed during the regeneration step.
 7. A method according to claim 1 includingsaid resin is a polymer having substituted ammonium functionality.
 8. A method according to claim 7 in whichsaid resin is a polymer having quaternary ammonium functionality.
 9. A method according to claim 1 in whichsaid resin is a strong base anion exchange resin.
 10. A method according to claim 9 includingproviding a bed of iodine crystals, continuously passing water through said iodine crystals to produce said iodine solution and continuously passing said iodine solution through said resin bed during the regeneration step.
 11. A method according to claim 9 includingproviding a bed of iodine crystals, continuously passing water through said iodine crystals to produce said iodine solution containing at least 1 mg. I₂ per liter, and continuously passing said iodine solution through said resin bed during the regeneration step.
 12. A method according to claim 9 includingproviding a bed of iodine crystals, and passing water through said iodine crystals to produce said iodine solution.
 13. A method according to claim 12 including switching the flow of water from a path through said resin bed when the iodine content is reduced to said selected lower level to a path through said bed of iodine crystals and then through said resin bed until said resin bed is re-iodinated, andwhen said resin bed is re-iodinated, switching the flow of water back to a path directly through said resin bed.
 14. A method according to claim 12 includingswitching the flow of water from a path through said resin bed when the iodine content is reduced to said selected lower level to a path through said bed of iodine crystals and then through said resin bed until said resin bed is re-iodinated, and when said resin bed is re-iodinated, switching the flow of water back to a path directly through said resin bed.
 15. A method according to claim 1 includingproviding a bed of iodine crystals, and passing water through said iodine crystals to produce said iodine solution.
 16. A method according to claim 15 comprising the additional steps ofagain continuing flowing water through said bed of anion exchange resin until the effluent iodine content is reduced to a selected lower level, again preparing an aqueous solution of iodine by passing water through said bed of iodine crystals, again passing said solution through said resin bed to re-iodinate said resin to said selected iodine content, and again flowing further amounts of water requiring purification through said iodinated anion exchange resin to remove iodine from said resin and produce said predetermined iodine residual therein.
 17. A method according to claim 15 includingswitching the flow of water from a path through said resin bed when the iodine content is reduced to said selected lower level to a path through said bed of iodine crystals and then through said resin bed until said resin bed is re-iodinated, and when said resin bed is re-iodinated, switching the flow of water back to a path directly through said resin bed.
 18. A method according to claim 17 in whichsaid switching of the path of water flow is by a three way valve positioned to direct flow to said resin bed or to said iodine crystals bed and thence to said resin bed.
 19. A method according to claim 18 in whichsaid three way valve is controlled by a timer.
 20. A method according to claim 18 in whichsaid three way valve is controlled by a sensor responsive to a selected volume of water passing through said resin bed.
 21. A method according to claim 18 in whichsaid three way valve is controlled by a sensor responsive to the I₂ residual in the water passing from said resin bed.
 22. An apparatus for continuous treatment of water to impart a predetermined residual of I₂ therein comprisinga bed of anion exchange resin iodinated to a selected iodine content and having an inlet and an outlet, a first conduit connected to the inlet of said anion exchange resin bed and connected to a source of water requiring treatment, a second conduit connected to said anion exchange resin bed outlet and comprising means for discharging treated water therefrom, a bed of iodine crystals having an inlet and an outlet, a third conduit connecting said iodine bed outlet to said first conduit, a fourth conduit connected to said iodine bed inlet and connected to said source of water, and valve means connected to said first conduit and said fourth conduit and to said source of water for directing flow of water to said second conduit selectively through said bed of iodine crystals and then through said resin bed via said fourth conduit or through only said resin bed via said first conduit.
 23. An apparatus according to claim 22 in whichsaid valve means comprises a three way valve connected between said source of water and said first and fourth conduits.
 24. An apparatus according to claim 23 includingautomatic means for operating said three way valve to change said direction of water flow after a selected amount of iodine has been eluted from said exchange resin bed.
 25. An apparatus according to claim 24 in whichsaid automatic means is a timer comprising means for actuating said three way valve after a selected time.
 26. An apparatus according to claim 24 in whichsaid automatic means includes a sensor responsive to the volume of water passing through said second conduit to actuate said three way valve after a selected volume of water has passed through said second conduit.
 27. An apparatus according to claim 24 in whichsaid automatic means includes a sensor responsive to the I₂ residual in water passing through said second conduit to actuate said three way valve when said I₂ residual has decreased to a selected level.
 28. A method of treating water to produce a predetermined I₂ residual therein comprisingproviding a bed of anion exchange resin iodinated to a selected iodine content, flowing water requiring purification through said iodinated anion exchange resin to remove iodine from said resin and produce said predetermined I₂ residual therein, continuing flowing said water through said bed of anion exchange resin until the effluent iodine content is reduced to a selected lower level, preparing in-situ an aqueous solution of I₂, passing said solution through said bed in-situ to re-iodinate said resin to said selected iodine content, and flowing further amounts of water requiring purification through said iodinated anion exchange resin to remove iodine from said resin and produce said predetermined I₂ residual therein. 